The present invention relates to a gut having a novel structure, and more particularly to a suitable gut for tennis rackets and badminton rackets or for strings of stringed musical instruments.
As to the prior arts, many kinds of guts made of thermoplastic resins have been proposed such as: those monofilaments having numerous spiral jogs on the surface of gut itself; those made of twisted monofilaments adhering mutually by thermoplastic rubber materials; and those made of twisted multi-filaments adhering mutually by thermal adhesion of thermoplastic material of the multi-filament at a stretched state.
However, the gut made of a monofilament of a synthetic resin has a disadvantage of becoming slack in use for a long period, and on the other hand, the gut comprising the above-mentioned monofilaments are not satisafactory in their durability and resistance to wear and they are expensive according to the production through complicate processes. As a more important problem, it is required that in the case where the gut is used for rackets for tennis or badminton, the gut has an excellent creep characteristic, so as not to become slack after use for a long period, high durability, waterproofness, and resistance to wear, and has a special very delicate material characteristic of having an appropriate friction on their surface, of giving a fine sound, a repulsion to the ball and a shock on the hand of the player.
However, in the prior art, such a gut fully satisfying these delicate material characteristics has not been proposed. The above-mentioned problems and other problems have been first solved effectively by the gut of the present invention summarized as follows.
A gut prepared by collectively twisting a plurality of monofilaments of thermoplastic resin(s) spinned from nozzles while maintaining said plurality of monofilaments at a temperature at least higher than the softening point of said resin(s).
In the more preferable case of the concrete Example of the present invention, the gut for rackets of tennis and badminton or for stringed musical instruments consists of a bundle of bristles prepared by twisting a bundle of thermoplastic resin filaments at a twist number of T of 3-100/m and having them mutually adhered while heating and superficially melting them, stretching after cooling, and heat-treating. The elongation at break of the gut is 10 to 40%.
At the time of the above-mentioned twisting, it is preferable to have the surface of each monofilament in a melt state and have the other sectional part of each monofilament in a semi-melt state. For that purpose, the filaments before assembling may be heated from outside. On twisting the bundle of the monofilaments in the above-mentioned state, the monofilaments mutually melt-adhered by both the heat which generates at assembling and their own latent heat to form a center part with a higher density and on the other hand, since the peripheral part of the bundle of monofilaments and the monofilaments present in the outermost periphery of the bundle are most easily able to radiate their heat, in other words, their heat is not so much maintained as the heat of filaments present in the center part of the bundle, the filaments in the peripheral part of the bundle mutually adhere while maintaining their own shape of monofilament.
Accordingly, the gut thus obtained has a novel structure consisting of the central strong nuclear part and the spiral peripheral part based on the monofilaments.
The gut of the present invention has the following advantages according to the above-mentioned novel structure and the continued steps of preparation of melt spinning, collective twisting, cooling, stretching, and heat-treating in that order.
That is, since the filaments are adhered mutually without using any adhesives the gut of the present invention has a good durability and resistance to wear, and since the gut of the present invention has in its periphery a spiral structure of monofilaments, it has an appropriate friction, and since the gut maintains a monofilamentous structure to a certain extent it is excellent in the creep characteristic. In addition, since the process of preparing the gut is not so complicated as in conventional guts comprising multifilament, the cost reduction is possible and its quality control is far easier than the conventional gut comprising multifilament. Moreover, by utilizing a polyvinylidene fluoride resin as the raw material it is possible to obtain gut excellent in mechanical strength and in weatherproofness.